Solid imaging method using multiphasic photohardenable compositions

ABSTRACT

An integral three-dimensional object is formed from a photohardenable liquid composition containing radiation deflecting matter.

FIELD OF THE INVENTION

This invention relates to production of three-dimensional objects byphotohardening, and more particularly to a method utilizingphotohardenable materials characterized by self limiting the depth ofphotohardening during irradiation.

BACKGROUND OF THE INVENTION

Many systems for production of three-dimensional modeling byphotohardening have been proposed. European Patent Application No.250,121 filed by Scitex Corp. Ltd. on June 6, 1987, provides a goodsummary of documents pertinent to this art area, including variousapproaches attributed to Hull, Kodama, and Herbert. Additionalbackground is described in U.S. Pat. No. 4,752,498 issued to Fudim onJune 21, 1988.

These approaches relate to the formation of solid sectors ofthree-dimensional objects in steps by sequential irradiation of areas orvolumes sought to be solidified. Various masking techniques aredescribed as well as the use of direct laser writing, i.e., exposing aphotohardenable polymer with a laser beam according to a desired patternand building a three-dimensional model layer by layer.

However, all these approaches fail to identify practical ways ofutilizing the advantages of vector scanning combined with means tomaintain constant exposure and attain substantially constant finalthickness of all hardened portions on each layer throughout the body ofthe rigid three-dimensional object. Furthermore, they fail to recognizevery important interrelations within specific ranges of operation, whichgovern the process and the apparatus parameters in order to render thempractical and useful. Such ranges are those of constant exposure levelsdependent on the photohardening response of the material, those ofminimum distance traveled by the beam at maximum acceleration dependenton the resolution and depth of photohardening, as well as those ofmaximum beam intensity depend on the photospeed of the photohardenablecomposition.

The Scitex patent, for example, suggests the use of photomasks or rasterscanning for achieving uniform exposure, but does not suggest a solutionfor keeping the exposure constant in the case of vector scanning. Theuse of photomasks renders such techniques excessively time consuming andexpensive. Raster scanning is also undesirable compared to vectorscanning for a number of reasons, including:

necessity to scan the whole field even if the object to be produced isonly a very small part of the total volume,

considerably increased amount of data to be stored in most cases,

overall more difficult manipulation of the stored data, and

the necessity to convert CAD-based vector data to raster data.

On the other hand, in the case of vector scanning only the areascorresponding to the shape of the rigid object have to be scanned, theamount of data to be stored is smaller the data can be manipulated moreeasily, and "more than 90% of the CAD based machines generate andutilize vector data" (Lasers & Optronics, January 1989, Vol. 8, No. 1,pg. 56). The main reason why laser vector scanning has not been utilizedPG,4 extensively so far is the fact that, despite its advantages, itintroduces problems related to the inertia of the optical members, suchas mirrors, of the available deflection systems for the currently mostconvenient actinic radiation sources, such as lasers. Since thesesystems are electromechanical in nature, there is a finite accelerationinvolved in reaching any beam velocity. This unavoidable non-uniformityin velocity results in unacceptable thickness variations. Especially inthe case of portions of layers having no immediate previous levels ofexposure at the high intensity it becomes necessary to use high beamvelocities, and therefore, longer acceleration times, which in turnresult in thickness non-uniformity. The use of low intensity lasers doesnot provide a good solution since it makes production of a solid objectexcessively time consuming. In addition, the usefulness of vectorscanning is further minimized unless at least the aforementioned depthand exposure level relationships are observed as evidenced under theDetailed Description of this invention.

No special attention has been paid so far to the composition itself byrelated art in the field of solid imaging, except in very general terms.

Thus, the compositions usually employed, present a number of differentproblems, a major one of which is excessive photohardening depthwiseusually accompanied by inadequate photohardening widthwise. This problembecomes especially severe in cantilevered or other areas of the rigidobject, which areas are not immediately over a substrate.

Therefore, it is an object of this invention to resolve the problemcited above by incorporating radiation deflecting matter in thephotohardenable composition in order to limit the depth ofphotohardening with simultaneous increase of the width ofphotohardening, so that the resolution is better balanced in alldirections.

European Patent Application 250,121 (Scitex Corp., Ltd.) discloses athree-dimensional modelling apparatus using a solidifiable liquid whichincludes radiation transparent particles in order to reduce shrinkage.

SUMMARY OF THE INVENTION

The instant invention is directed to methods for direct production ofthree-dimensional photohardened solid objects, layer by layer usingactinic radiation, preferably in a beam form such as provided by lasersfor direct writing, by utilizing photohardenable compositions, whichcontain radiation deflection matter in order to limit the depth ofphotohardening with simultaneous increase of the width ofphotohardening, so that the resolution is better balanced in alldirections. The integrity of the integral three-dimensional objects orparts thus formed is also highly improved.

This invention may be summarized as follows:

A method for accurately fabricating an integral three-dimensional objectfrom successive layers of a photohardenable liquid compositioncomprising the steps of:

(a) forming a layer of a photohardenable liquid;

(b) photohardening at least a portion of the layer of photohardenableliquid by exposure to actinic radiation;

(c) introducing a new layer of photohardenable liquid onto the layerpreviously exposed to actinic radiation;

(d) photohardening at least a portion of the new liquid layer byexposure to actinic radiation, with the requirement that thephotohardenable composition comprises an ethylenically unsaturatedmonomer, a photoinitiator, and radiation deflecting matter, thedeflecting matter having a first index of refraction, and the rest ofthe composition having a second index of refraction, the absolute valueof the difference between the first index of refraction and the secondindex of refraction being different than zero.

BRIEF DESCRIPTION OF THE DRAWING

The reader's understanding of practical implementation of preferredembodiments of the invention will be enhanced by reference to thefollowing detailed description taken in conjunction with perusal of thedrawing FIGURE, wherein:

FIG. 1 is a block diagram of an apparatus used to perform the preferredembodiment of the process of the instant invention.

FIG. 2 shows a typical relationship between depth of photohardening andexposure in the case of a clear photohardenable composition.

FIG. 3 shows a typical relationship between depth of photohardening andexposure in the case of a photohardenable composition containingradiation deflecting matter.

FIG. 4 shows the relationship between depth of photohardening andexposure in the case of the same photohardenable composition shown inFIG. 3 with no radiation deflecting matter contained therein.

FIG. 5 shows a typical relationship between depth of photohardening andexposure in the case of a photohardenable composition containingradiation deflection matter.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention is directed to methods for direct production ofthree-dimensional photohardened solid objects, layer by layer usingactinic radiation, preferably in a beam form such as provided by lasersfor direct writing, by using photohardenable compositions comprising anethylenically unsaturated monomer, a photoinitiator, and radiationdeflecting matter, the deflecting matter having a first index ofrefraction, and the rest of the composition having a second index ofrefraction, the absolute value of the difference between the first indexof refraction and the second index of refraction being different thanzero.

As aforementioned, many systems for production of three-dimensionalmodeling by photohardening have been proposed. European PatentApplication No. 250,121 filed by Scitex Corp. Ltd. on June 6, 1987,provides a good summary of documents pertinent to this art area,including various approaches attributed to Hull, Kodama, and Herbert.Additional background is described in U.S. Pat. No. 4,752,498 issued toFudim on June 21, 1988.

In a preferred embodiment, an apparatus for practicing the presentinvention is depicted in FIG. 1, in the form of a block diagram. Theapparatus and its operation are described below.

Actinic radiation means 10 shown in FIG. 1, which is preferably a highpower laser, is used to provide an actinic radiation beam 12 having acertain intensity. The radiation beam 12 is passed through a modulator14, where its intensity may be modulated. The modulated beam 12' ispassed in turn through deflection means 16 such as a vector scanner inthe form of a two-mirror 20 and 22 assembly, each mirror separatelydriven by a different motor 24 and 26 respectively. By causing mirror 20driven by motor 24 to turn, the beam is deflected in an X direction,while by causing mirror 22 to turn, the beam is deflected in a Ydirection, X direction being perpendicular to the Y direction. Theactinic radiation beam 12" is thus controllably deflected towardspreselected portions of the photohardenable composition which iscontained in vessel 44 and presents a surface 46. It photohardens a thinlayer 48 closest to the surface 46 of a photohardenable composition 40,to a depth of photohardening which equals the maximum thickness of thelayer 48. The composite movement of the beam is preferably a vector typemovement, and the beam is said to move or be scanned in a vector mode.Due to the inertia of the electromechanical deflection means 16, thevelocity of the beam 12" on the thin layer 48 is also limited by theinertia and the electromechanical nature of the deflection means 16.

The deflection of the two mirrors 20 and 22 through motors 24 and 26respectively is controlled by the second computer control means 34,while the graphic data corresponding to the shape of the solid objectunder production are stored in the first computer control means 30.

The second computer control means 34 is coupled with the modulationmeans 14, the deflection means 16, and the first computer control means30, through control/feedback lines 50, 54, and 58, respectively. Thedata stored in computer control means 30 are fed to computer controlmeans 34, and after being processed cause motors 24 and 26 to turn andmove mirrors 20 and 22 accordingly in order to deflect the beam towardspredetermined positions on the thin layer 48. Electrical feedbackregarding the relative movements of the mirrors 20 and 22 is provided bythe deflection means to the second computer control means 34 throughline 54.

The manner of introducing successive layers of photohardenable liquidand exposing to actinic radiation such as a laser will generally be bytwo methods. In a first method a pool of liquid is present in a vesseland it is not necessary to introduce additional photohardenable liquid.In such case a movable table or floor supports the liquid. Initially thetable or floor is elevated with a portion of the photohardenable liquidpresent above the table or floor and a portion of the liquid present inthe vessel around the edge of the table or floor and/or underneath it.(Illustratively a table is present which allows liquid to flowunderneath the table as it is used.) After exposure and photohardeningof a portion of the liquid layer above the table, the table is loweredto allow another layer of photohardenable liquid to flow on top of theprevious layer followed by exposure of predetermined area on the newlyapplied liquid layer. If necessary due to the shape of the finalthree-dimensional article the thickness of more than one liquid layercan be photohardened. This procedure of table or floor lowering andexposure continues until formation of the desired three-dimensionalarticle occurs.

In a second method a movable table or floor need not be employed butrather a new quantity of photohardenable liquid is introduced into avessel after an exposure step in formation of a new liquid layer on apreviously exposed layer containing both photohardened liquidphotohardenable material. Criticality is not present in the manner ofliquid introduction but rather in an ability to photoharden successiveliquid layers.

In FIG. 1, a movable table 41 is initially positioned within thephotohardenable composition 40, a short predetermined distance from thesurface 46, providing a thin layer 48 between the surface 46 and thetable 41. The positioning of the table is provided by the placementmeans 42, which in turn is controlled by the first computer controlmeans 30 according to the data stored therein. The graphic datacorresponding to the first layer of the shape of the rigid object arefed from computer control means 30 to computer control means 34, wherethey are processed along with feedback data obtained from deflectingmeans 16, and are fed to modulator 14 for controlling the same, so thatwhen the beam travels in a vector mode on predetermined portions of thethin layer 48, the exposure remains constant.

When the first layer of the rigid object is complete, the movable table41 is lowered by a small predetermined distance by the placement means42 through a command from first computer control means 30. Following asimilar command from computer means 30, layer forming means, such asdoctor knife 43 sweeps the surface 46 for leveling purposes. The sameprocedure is then followed for producing the second, third, and thefollowing layers until the rigid object is completed.

In the discussions above and below, the actinic radiation, preferably inthe form of a beam, and more preferably in the form of a laser beam, ismany times referred to as light, or it is given other connotations. Thisis done to make the discussion clearer in view of the particular examplebeing described. Thus, it should not be taken as restricting the scopeand limits of this invention. Nevertheless, the preferred actinicradiation is light, including ultraviolet (UV), visible, and infrared(IR) light. From these three wavelength regions of light, ultraviolet iseven more preferred.

The formulation of the photohardenable compositions for solid imagingpurposes is very important in order to receive the desirable effects andcharacteristics, regardless of whether the scanning is of the vectortype, raster type, or any other type, and the discussion hereinafter isreferred to in any type of scanning, unless otherwise stated. However,from the different types of scanning, the vector type is the preferredtype of scanning.

A photohardenable composition for solid imaging should contain at leastone photohardenable monomer or oligomer and at least one photoinitiator.For the purposes of this invention, the words monomer and oligomer havesubstantially the same meaning and they may be used interchangeably.

Examples of suitable monomers which can be used alone or in combinationwith other monomers include tbutyl acrylate and methacrylate,1,5-pentanediol diacrylate and dimethacrylate, N,N-diethylaminoethylacrylate and methacrylate, ethylene glycol diacrylate anddimethacrylate, 1,4-butanediol diacrylate and dimethacrylate, diethyleneglycol diacrylate and dimethacrylate, hexamethylene glycol diacrylateand dimethacrylate, 1,3-propanediol diacrylate and dimethacrylate,decamethylene glycol diacrylate and dimethacrylate, 1,4-cyclohexanedioldiacrylate and dimethacrylate, 2,2-dimethylolpropane diacrylate anddimethacrylate, glycerol diacrylate and dimethacrylate, tripropyleneglycol diacrylate and dimethacrylate, glycerol triacrylate andtrimethacrylate, trimethylolpropane triacrylate and trimethacrylate,pentaerythritol triacrylate and trimethacrylate, polyoxyethylatedtrimethylolpropane triacrylate and trimethacrylate and similar compoundsas disclosed in U.S. Pat. No. 3,380,831, 2,2-di(p-hydroxyphenyl)-propanediacrylate, pentaerythritol tetraacrylate and tetramethacrylate,2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycoldiacrylate, polyoxyethyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate,di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-methacryloxyethyl) ether of bisphenol-A,di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-acryloxyethyl) ether of bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol, triethyleneglycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate,butylene glycol diacrylate and dimethacrylate, 1,2,4-butanetrioltriacrylate and trimethacrylate, 2,2,4-trimethyl-1,3-pentanedioldiacrylate and dimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate,diallyl fumarate, styrene, 1,4-benzenediol dimethacrylate,1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl benzene. Also usefulare ethylenically unsaturated compounds having a molecular weight of atleast 300, e.g., alkylene or a polyalkylene glycol diacrylate preparedfrom an alkylene glycol of 2 to 15 carbons or a polyalkylene etherglycol of 1 to 10 ether linkages, and those disclosed in U.S. Pat. No.2,927,022, e.g., those having a plurality of addition polymerizableethylenic linkages particularly when present as terminal linkages.Particularly preferred monomers are ethoxylated trimethylolpropanetriacrylate, ethylated pentaerythritol triacrylate, dipentaerythritolmonohydroxypentaacrylate, 1,10-decanediol dimethylacrylate,di-(3-acryloxy-2-hydroxylpropyl)ether of bisphenol A oligomers,di-(3-methacryloxy-2-hydroxyl alkyl)ether of bisphenol A oligomers,urethane diacrylates and methacrylates and oligomers thereof,coprolactone acrylates and methacrylates, propoxylated neopentyl glycoldiacrylate and methacrylate, and mixtures thereof.

Examples of photoinitiators which are useful in the present inventionalone or in combination are described in U.S. Pat. No. 2,760,863 andinclude vicinal ketaldonyl alcohols such as benzoin, pivaloin, acyloinethers, e.g., benzoin methyl and ethyl ethers, benzil dimethyl ketal;α-hydrocarbon-substituted aromatic acyloins, including α-methylbenzoinα-allylbenzoin, α-phenylbenzoin, 1-hydroxylcyclohexyl phenol ketone,diethoxyphenol acetophenone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propanone-1.Photoreducible dyes and reducing agents disclosed in U.S. Pat. Nos.2,850,445, 2,875,047, 3,097,096, 3,074,974, 3,097,097 and 3,145,104, aswell as dyes of the phenazine, oxazine, and quinone classes, Michler'sketone, benzophenone, acryloxy benzophenone, 2,4,5-triphenylimidazolyldimers with hydrogen donors including leuco dyes and mixtures thereof asdescribed in U.S. Pat. Nos. 3,427,161, 3,479,185 and 3,549,367 can beused as initiators. Also useful with photoinitiators are sensitizersdisclosed in U.S. Pat No. 4,162,162. The photoinitiator orphotoinitiator system is present in 0.05 to 10% by weight based on thetotal weight of the photohardenable composition. Other suitablephotoinitiation systems which are thermally inactive but which generatefree radicals upon exposure to actinic light at or below 185° C. includethe substituted or unsubstituted polynuclear quinones which arecompounds having two intracyclic carbon atoms in a conjugatedcarbocyclic ring system, e.g., 9,10-anthraquinone,2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone,octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthraquinone,benz(a)anthracene-7,12-dione, 2,3-naphthacene-5,12-dione,2-methyl-1,4-naphthoquinone, 1,4-dimethyl-anthraquinone,2,3-dimethylanthraquinone, 2-phenylanthraquinone,2,3-diphenylanthraquinone, retenequinone,7,8,9,10-tetrahydronaphthacene-5,12-dione, and1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione; also, alpha aminoaromatic ketones, halogenated compounds like Trichloromethyl substitutedcyclohexadienones and triazines or chlorinated acetophenone derivatives,thioxanthones in presence of tertiary amines, and titanocenes.

Although the preferred mechanism of photohardening is free radicalpolymerization, other mechanisms of photohardening apply also within therealm of this invention. Such other mechanisms include but are notlimited to cationic polymerization, anionic polymerization, condensationpolymerization, addition polymerization, and the like.

Other components may also be present in the photohardenablecompositions, e.g., pigments, dyes, extenders, thermal inhibitors,interlayer and generally interfacial adhesion promoters, such asorganosilane coupling agents, dispersants, surfactants, plasticizers,coating aids such as polyethylene oxides, etc. so long as thephotohardenable compositions retain their essential properties. Theplasticizers can be liquid or solid as well as polymeric in nature.Examples of plasticizers are diethyl phthalate, dibutyl phthalate, butylbenzyl phthalate, dibenzyl phthalate, alkyl phosphates, polyalkyleneglycols, glycerol, poly(ethylene oxides), hydroxy ethylated alkylphenol, tricresyl phosphate, triethyleneglycol diacetate, triethyleneglycol caprate - caprylate, dioctyl phthalate and polyesterplasticizers.

In this discussion a clear distinction should be made between aphotohardenable and a photohardened composition. The former refers toone which has not yet been subjected to irradiation, while the latterrefers to one which has been photohardened by irradiation.

The instant invention is intended for solid imaging techniques which usephotohardenable compositions comprising an ethylenically unsaturatedmonomer, a photoinitiator, and radiation deflecting matter, thedeflecting matter having a first index of refraction, and the rest ofthe composition having a second index of refraction, the absolute valueof the difference between the first index of refraction and the secondindex of refraction being different than zero.

When the composition is clear to the radiation beam, the depth ofphotohardening is considerably larger than the width of photohardening,mainly because the beams utilized, such as laser beams, and the like,are well collimated and focused. Addition of inert particulate matter,which is transparent to the radiation in the environment of thecomposition, has certain well recognized advantages, such as reductionof shrinkage upon polymerization or photohardening in general, and oftenincrease in photospeed due to the reduction of the amount of activecomposition, which is subject to shrinkage, per unit of volume.

The large depth of photohardening is not a very big problem in areassupported by a substrate, since the depth is determined primarily by thethickness of the liquid layer on top of the substrate. However, incantilevered unsupported areas, where the thickness of the liquid isvery large, it becomes a serious disadvantage, as the depth ofphotohardening is not controlled or limited any more by the substrate.This is actually the area where the differences between conventional twodimensional imaging and solid or three-dimensional imaging manifestthemselves as being most profound. This is particularly important whenthere are uncontrollable exposure variations, which may result inthickness variations, and poor resolution. Thus a way to control thethickness is needed.

In addition to the lack of control of the depth of photohardening, thereis one more problem having to do with resolution considerations. Exceptin very limited occasions, it is highly desirable for the resolution ortolerances of a part to be comparable in all dimensions. It does notmake much sense to have high resolution in one dimension and very poorresolution in another dimension since the final resolution is going tobe necessarily considered as poor, except in rare occasions as mentionedabove. In clear compositions, the depth to width ratio is high, and thusthe resolution widthwise is accordingly higher than the resolutiondepthwise. As a matter of fact, the resolution is inversely proportionalto the dimensional units, and therefore, if the depth to width ratio isfor example 5, the width resolution will be five times better than thedepth resolution, when other factors do not play an active role. Thus,high transparency of the composition becomes in general undesirable.Preferable regions of depth to width ratios are 7:1 to 1:1, and morepreferable 3:1 to 1:1.

The task of reducing the transparency or in other words increasing theoptical density, also referred to as opacity, of the photohardenablecomposition sounds as a rather straightforward one, and it is, ifphotospeed and other important parameters are not taken into account.For example, addition of a radiation absorbent in the composition willdecrease the depth of photohardening without affecting considerably thewidth. Typical absorbents are dyes. The monomers or oligomers of thecomposition may also act as absorbants to different degrees. However, ifa dye, or other absorbent is used, the part of the radiation which isabsorbed by it will not be available to directly promote photohardening.

Considering now the photoinitiator as means of absorption to reduce thedepth of photohardening, it should be realized that in order for this tohappen a certain high content in photoinitiator has to be exceeded. Asthe content in photoinitiator in the composition increases from zeroincrementally, the photospeed increases but at the same time the depthalso increases since low starving areas at the bottom of the depth ofphotohardening form now more polymer due to the increase in number offree radicals. Only when the radiation starts being intercepted to aconsiderable degree by an excessive amount of photoinitiator, will thedepth of photohardening start decreasing. However, the properties of thephotohardened object will start deteriorating. This is because as theconcentration of free radicals being formed increases the molecularweight decreases, and therefore the structural properties deteriorate.At the same time, in the plethora of free radicals, the free radicalsmay start combining with each other and just absorb energy withoutfulfilling their role of photoinitiation. Thus, although the amount ofphotoinitiator can in a limited way serve as means for controlling thedepth of photohardening, other undesirable phenomena occurringsimultaneously, decrease considerably its usefulness when employed onlyby itself for this purpose.

According to this invention, a separate phase of dispersed particulatesolid matter and emulsified liquid matter may be utilized to control thedepth/width relation, under certain conditions, which involve refractionor reflection or scattering of light or any combination thereof,labelled as radiation deflection for the purposes of this discussion. Ifeverything else is kept constant, as the content in separate phase ofradiation deflecting matter is increased, so does the width in expenseof the depth. Since the radiation is not absorbed but just deflected, noconsiderable loss of radiation occurs, and therefore, there is nosubstantial loss of photospeed. Thus, the radiation deflective matterwhich may be utilized in the preferred embodiments of this invention issubstantially non-transparent in the environment of the photohardenablecomposition, since it gives opacity to the same.

It is essential to note that the phenomena of transparency, andnon-transparency (translucence, opacity, absorbance) are only importantwhen examined in the environment and conditions within the limits ofwhich they occur. A powder for example dispersed in a medium, istransparent to radiation if not only it does not absorb inherently theradiation, but also if it has substantially the same index of refractionas the medium so that no light deflection takes place at or around theinterface of each particle of the powder and the medium. The samepowder, when dispersed in a liquid of substantially different refractionindex, it will appear as translucent or opaque (hindering at least partof the light to travel directly through the medium containing thepowder); in other words it will appear as non-transparent. Thus,translucence and opacity may have similar end results as absorbanceregarding amount of light passing through.

The amount of light-deflecting matter to give optimum properties to thephotohardenable composition is a function of a number of factors, asshown below, as well as of the balance of gains and compromises thatconstitute what is considered to be "optimum" at the time, depending onthe particular circumstances. Thus, it would not be appropriate toattempt to give absolute numbers in order to show how one can achieveoptimum properties. It would rather be much more accurate to show theinterrelationships governing these factors, in order to allow a personskilled in the art to practice this invention and select a set ofproperties that he or she would consider optimum for the desired result.It is preferable that there is an adequate amount of radiationdeflecting matter in the composition to reduce the depth ofphotohardening by at least 10%, more preferably at least by 20%, andeven more preferably at least by 40%. It is also preferable that thedepth to width ratio does not increase by such addition. In any case,the amount of light deflecting matter may be from 5% to 70 % by weight,depending on the degree of deflection that it may provide. In lessextreme cases with regard to both particle size and refraction index, itwould be preferable for the amount of the deflecting matter in thecomposition to range within 10% and 60%, and most preferable within 20%and 50% by weight. As mentioned before, matter such as radiationdeflecting matter is desirable also for reducing shrinkage andincreasing photospeed.

Initially, if we call "particle" each individual unit of the separatephase of the dispersed or emulsified matter in the photohardenablecomposition as aforementioned, the maximum particle size, measured asthe average particle diameter, should be smaller than the depth ofphotohardening, but not width necessarily. It is preferred that not onlysubstantially all particles are smaller than the depth ofphotohardening, but also that at least 90% of the particles are smallerthan half the depth of photohardening, and even more preferred that atleast 90% of the particles are smaller than one tenth the depth ofphotohardening.

In order to be effective for their purpose, the majority of particlesshould also be preferably larger than approximately half the wavelengthof the beam's radiation. At approximately half the wavelength, thescattering yield of the particles attains a maximum value, while itdecreases rapidly as the size of the particles goes down. On the otherhand, as the particle size increases over about half the wavelength ofthe radiation, the scattering yield also starts dropping, but at a lowerpace. As the particle size increases even more, the phenomena ofrefraction and reflection start prevailing. In practice there are onlylimited situations where all particles have substantially the same size,in which case they are called monodisperse. Generally, there is adistribution of particle sizes providing a combination of all types ofactinic-radiation deflection. Taking into account also that the higherthe refractive index of the particle the higher the scattering, one canpractically achieve any desired opacity, by lowering or raising thecontent in deflecting matter, which in turn will control the depth ofphotohardening.

The separate phase of the deflection matter should have a differentrefraction index than that of the rest of the photohardenablecomposition. The two refraction indices should preferably be differingby at least 0.01, more preferably by at least 0.02, and even morepreferably by at least 0.04.

It is also preferable that the refraction index of the phase of thedeflection matter is higher than that of the photohardenablecomposition, and the mixture gives even higher refraction indexdifferences upon exposure, as long as it falls within the abovelimitations. Higher photospeed is obtained.

There are instances where the initially opaque composition may becomeless opaque or even substantially transparent after exposure. Thiscondition is less desirable, and in order to be operable in terms ofthis invention, it will require considerably larger amounts of radiationdeflecting matter.

Reduction of the depth of photohardening to a desired level takes placewith:

increased difference between the refractive index of the compositioncontaining no radiation deflecting matter and the deflecting matteritself;

increased content in radiation deflecting matter; decrease particlesize;

increased difference in refractive index due to the result of actinicradiation.

Solid deflecting materials that may be employed in the photohardenablecomposition are powders falling within the ranges of particle size andrequirements needed for the refraction indices mentioned above. Theyinclude particulate organic polymeric compounds which are substantiallyinsoluble in the photohardenable composition, and particulate inorganiccompounds which are also substantially insoluble in the photohardenablecomposition. Oxygen bearing inorganic compounds such as relativelynon-reactive oxides and hydroxides are preferable. Carbides and nitridesmay also be used, as well as fluorides such as calcium fluoride.

Examples of preferred organic polymeric compounds are crosslinked mono-or multifunctional monomers, such as the ones given above in the list ofexemplary monomers usable within the scope of this invention,polyamides, polyimides, fluoropolymers, and mixtures thereof. Ofparticular preference are crosslinked polyacrylates, polymethacrylates,as in U.S. Pat. No. 4,414,278, polytetrafluoroethylene,polyfluoroethylenepropylene, copolymers of perfluoroalkoxyfluoroethylene and tetrafluoroethylene, polyethylene, polypropylene, andmixtures thereof, as well as powdered engineering plastics.

Examples of preferred inorganic compounds are as aforementioned, not tooreactive oxides and hydroxides, such as the oxides and hydroxides ofaluminum, silicon, magnesium, zinc, zirconium, and chemical or physicalmixtures thereof. A chemical mixture is a distinct and differentcompound, such as aluminum silicate in the case of aluminum oxide andsilicon oxide, while a physical mixture of these two oxides is theunreacted combination of silicon oxide with aluminum oxide. Other morereactive oxides and hydroxides, such as those of the alkalis and thealkaline earths may be used in chemical mixtures of oxides andhydroxides, as long as the chemical mixture becomes reasonablynon-reactive. Calcium aluminosilicate for example is a chemical mixtureof calcium oxide, silicon oxide and aluminum oxide, which is notreactive, but contains reactive calcium oxide in a chemical mixtureConventional glasses are also good examples of inert chemical mixtures,which nevertheless contain both reactive and relatively non-reactiveoxides. Carbonates, and especially those of the alkaline earths are alsouseful for the practice of the instant invention

Dispersants used to disperse solid deflecting matter and emulsifiers toemulsify liquid deflecting matter in the photohardenable compositionalso play an important role regarding uniformity, stability, and thelike. They may also influence the particle or micelle size and thereforethe behavior of the composition towards its radiation deflectionproperties.

FIGS. 3 and 5 show the effect of radiation deflecting matter on thedepth of photohardening. As the exposure increases, the depth isapproaching a plateau. In the case of clear compositions, as shown inFIG. 2, corresponding to the sample of Example 2, there is no suchplateau within the examined regions of exposure. Due to refraction indexconsiderations, as discussed earlier, the content in radiationdeflecting matter has to be increased in the case of crosslinkedTrimethylol propane triacrylate (TMPTA) in monomeric TMPTA in order togive appreciable self limiting characteristics to the depth ofphotohardening (Example 5).

Examples of photohardenable compositions are given below forillustration purposes only, and should not be construed as restrictingthe scope or limits of this invention. Quantities are given by weight ingrams.

EXAMPLE 1 (Sample preparation)

The samples described in the Examples cited below, were prepared asfollows:

The photohardenable composition was poured into a stainless steel squarecavity (1 3/4"×1 3/4"×110 mils thick). The excess liquid was removed bya doctor knife blade. The liquid was exposed with a rectangular pattern(1 9/16"×1 1/2") using an argon ion laser beam at 350-360 nm wavelengthsas described above.

After exposure, the solidified pattern was removed from the cavity witha pair of tweezers, and then blotted dry. The thickness of the patternwas measured and plotted against different exposure levels.

Other pertinent observations were also made.

EXAMPLE 2

The following ingredients were mixed with a mechanical mixer until ahomogeneous mixture was received:

    ______________________________________                                        Novacure 3704 (monomer)                                                                              50                                                     (Bisphenol A bis(2-hydroxypropyl)                                             diacrylate)                                                                   TMPTA (Monomer) (Trimethylol                                                                         50                                                     propane triacrylate)                                                          Irgacure 651 by Ciba Geigy                                                                           1.6                                                    (initiator) (2,2-dimethoxy                                                    2-phenylacetophenone)                                                         ______________________________________                                    

A sample was made as described in Example 1. The relation of depth ofphotohardening versus exposure is shown in FIG. 2. The exposed sampleremained clear.

EXAMPLE 3

The following ingredients were mixed with a mechanical mixer until ahomogeneous mixture was received:

    ______________________________________                                        Novacure 3704 (Bisphenol A                                                                              40                                                  bis(2-hydroxypropyl) diacrylate                                               TMPTA (Trimethylol Propane Triacrylate)                                                                 40                                                  Plasthall 4141 (CP Hall Company)                                                                        20                                                  (Triethylene glycol caprate - caprylate)                                      Irgacure 651 (2,2-dimethoxy-2                                                                           1.6                                                 phenylacetophenone)                                                           ______________________________________                                    

A sample was made as described in Example 1. The relationship betweenDepth of photohardening and exposure is shown in FIG. 4.

EXAMPLE 4

The following ingredients were mixed in a Waring Blender at high speedfor 2 minutes, and the mixture was allowed to degas:

    ______________________________________                                        Novacure 3704 (Bisphenol A bis(2-                                                                      24.0                                                 hydroxypropyl) diacrylate)                                                    TMPTA (Trimethylol Propane                                                                             24.0                                                 Triacrylate)                                                                  Plasthall 4141 (Triethylene glycol                                                                     12.0                                                 caprate - caprylate)                                                          Triton X-100 (Octyl phenol poly                                                                        0.8                                                  ether alcohol)                                                                Crosslinked TMPTA beads (Prepared as                                                                   40.0                                                 described in Example 2 of U.S.                                                Pat. No. 4,414,278)                                                           Irgacure 651 (2,2-dimethoxy-2                                                                          1.6                                                  phenylacetophenone)                                                           ______________________________________                                    

A sample was made as described in Example 1. The relationship betweenDepth of photohardening and exposure is shown in FIG. 3. The sample wasopaque before and after photohardening.

EXAMPLE 5

The following ingredients were mixed with a mechanical mixer until ahomogeneous mixture was received:

    ______________________________________                                        TMPTA (Trimethylol Propane                                                                             60.0                                                 Triacrylate)                                                                  Crosslinked TMPTA beads (Prepared as                                                                   40.0                                                 described in Example 2 of U.S.                                                Pat. No. 4,414,278)                                                           Irgacure 651 (2,2-dimethoxy-2-phenylaceto-                                                             0.4                                                  phenone)                                                                      ______________________________________                                    

A sample was made as described in Example 1. The relationship betweenDepth of photohardening and exposure is shown in FIG. 5. The sample wasopaque before and after photohardening.

    ______________________________________                                        EXAMPLES 6A TO 6C                                                                                6A     6B     6C                                           ______________________________________                                        Novacure 3704 [Bisphenol A bis(2-                                                                  50.0     50.0   50.0                                     hydroxypropyl) diacrylate]                                                    TMPTA (Trimethylol Propane                                                                         50.0     50.0   50.0                                     Triacrylate)                                                                  Triton X-100 (Octyl Phenol                                                                         1.0      1.0    1.0                                      polyether alcohol)                                                            Irgacure 651 (2,2-dimethoxy-2-                                                                     0.93     0.6    0.54                                     phenylacetophenone                                                            alpha-Alumina (average particle                                                                    132.0    --     --                                       size 2.4 micrometers by ALCOA                                                 Polytetrafluoroethylene powder                                                                     --       50.0   --                                       (average particle size 3.0                                                    micrometers by MicroPowders, Inc.                                             Polyethylene powder (average                                                                       --       --     33.0                                     particle size 2 micrometers, by                                               Dura Commodities Corporation)                                                 ______________________________________                                    

The above ingredients were mixed with a Waring blender at maximum speedfor 2 minutes.

The samples prepared above were subjected to the conditions ofExample 1. The minimum exposure required to give an integral film was8.6 mJ/cm² in the case of 6A, 17.4 mJ/cm² in case 6B, and 32.5 mJ/cm² inthe case of 6C.

All samples gave self-limiting characteristics regarding depth ofphotohardening. They were opaque before and after exposure. Sample 6Agave excellent photospeed as shown above.

EXAMPLE 7

A three-dimensional object was made for 50 successive layers of thecomposition described in Example 4, by using the method of thisinvention. An argon ion laser at 350-360 nm wavelength was utilized asthe radiation source. The diameter of the laser beam was 5 thousands ofone inch. Each layer had a thickness of 10 thousandths of one inch.

What is claimed is:
 1. A method for accurately fabricating an integralthree-dimensional object from successive layers of a photohardenableliquid composition comprising the steps of:(a) forming a layer of aphotohardenable liquid; (b) photohardening at least a portion of thelayer of photohardenable liquid by exposure to actinic radiation; (c)introducing a new layer of photohardenable liquid onto the layerpreviously exposed to actinic radiation; and (d) photohardening at leasta portion of the new liquid layer by exposure to actinic radiation, withthe requirement that the photohardenable composition comprises anethylenically unsaturated monomer, photoinitiator, and radiationdeflecting matter selected from the group consisting of an emulsifiedliquid, a solid which is substantially insoluble in the photohardenablecomposition and combination thereof, the deflecting matter deflectingthe actinic radiation and having a first index of refraction, theremainder of the composition except for the deflecting matter having asecond index of refraction, the absolute value of the difference betweenthe first index of refraction and the second index of refraction beinggreater than 0.01.
 2. The method of claim 1 wherein steps (c) and (d)are successively repeated.
 3. The method of claim 2, wherein the actinicradiation is in the form of a beam.
 4. The method of claim 3, whereinthe beam is a laser beam.
 5. The method of claim 2, wherein thedeflecting matter is an emulsified liquid.
 6. The method of claim 2,wherein the deflecting matter is a dispersed solid.
 7. The method ofclaim 2, wherein the dispersed solid comprises a particulate organicpolymeric compound.
 8. The method of claim 2, wherein the dispersedsolid comprises a particulate inorganic compound.
 9. The method of claim2, wherein the inorganic compound contains chemically bound oxygen. 10.The method of claim 9, wherein the inorganic compound is selected fromthe group consisting of oxides and hydroxides of aluminum, silicon,magnesium, zinc, zirconium, and mixtures thereof.
 11. The method ofclaim 2 wherein the deflection matter comprises a combination ofemulsified liquid and dispersed solid.
 12. The method of claim 2 whereinthe deflection matter has higher refractive index than the rest of thecomposition.
 13. A three-dimensional solid part obtained by the methodof claim 2.